479,819 research outputs found
Synthesis and characterization by FTIR spectroscopy of silica aerogels prepared using several Si(OR)4 and R′′Si(OR′)3 precursors
No full textWe report the synthesis and Fourier Transform Infrared spectroscopy characterization results dealing with the surface modification of silica aerogels obtained via a two-step sol-gel process where various silicon precursors and co-precursors were used. The hydrolysis and poly-condensation steps were followed by carbon dioxide supercritical drying (Tc = 31.1 °C; Pc = 73.7 bar). The silicon precursors contain four identical hydrolysable alkoxy groups (methoxy or ethoxy), while in the co-precursors, one of the alkoxy groups is substituted by a non-hydrolysable alkyl group (methyl, ethyl, n-propyl, iso-butyl, n-octyl, vinyl or phenyl). Identically, surface-functionalized silica aerogels were obtained from various silicon precursor-co-precursor combinations and their chemical structures were compared. The infrared spectroscopy revealed the existence of chemically comparable solid networks with some differences due to the nature of the silicon precursors. © 2008 Elsevier B.V. All rights reserved.BERTOLUZZA A, 1982, J NON-CRYST SOLIDS, V48, P117, DOI 10.1016-0022-3093(82)90250-2; Bhagat SD, 2007, MICROPOR MESOPOR MAT, V100, P350, DOI 10.1016-j.micromeso.2006.10.026; Brinker C.J., 1990, SOL GEL SCI, P581; CAM Mulder, 1986, AEROGELS, P68; CANTIN M, 1974, NUCL INSTRUM METHODS, V118, P177, DOI 10.1016-0029-554X(74)90700-9; CHMEL A, 1990, J NON-CRYST SOLIDS, V122, P285, DOI 10.1016-0022-3093(90)90993-V; Colthup N.B., 1975, INTRO INFRARED RAMAN, P257; DURAN A, 1986, J NON-CRYST SOLIDS, V82, P69, DOI 10.1016-0022-3093(86)90112-2; El Rassy H, 2005, J NON-CRYST SOLIDS, V351, P1603, DOI 10.1016-j.jnoncrysol.2005.03.048; Forest L, 1998, J NON-CRYST SOLIDS, V225, P287, DOI 10.1016-S0022-3093(98)00325-1; Gopal NO, 2004, SPECTROCHIM ACTA A, V60, P2441, DOI 10.1016-j.saa.2003.12.021; Guise M.T., 1995, J NONCRYST SOLIDS, V186, P317; Gunzler H., 2002, IR SPECTROSCOPY INTR, P178; Hegde ND, 2006, APPL SURF SCI, V253, P1566, DOI 10.1016-j.apsusc.2006.02.036; Jones CW, 1998, NATURE, V393, P52; Matko S, 2005, POLYM DEGRAD STABIL, V88, P138, DOI 10.1016-j.polymdegradstab.2004.02.023; Novak Z, 2003, J SUPERCRIT FLUID, V27, P169, DOI 10.1016-S0896-8446(02)00233-4; Ou DL, 1997, J NON-CRYST SOLIDS, V210, P187, DOI 10.1016-S0022-3093(96)00585-6; PAJONK GM, 1991, APPL CATAL, V72, P217, DOI 10.1016-0166-9834(91)85054-Y; Rao AV, 2003, APPL SURF SCI, V206, P262, DOI 10.1016-S0169-4332(02)01232-1; Rao AV, 2001, J NON-CRYST SOLIDS, V285, P202; REED ST, 1990, SPIE, V1328, P220; ROA AV, 2004, J NONCRYST SOLIDS, V350, P216; Schwertfeger F, 1994, J SOL-GEL SCI TECHN, V2, P103, DOI 10.1007-BF00486221; Socrates G., 2001, INFRARED RAMAN CHARA, P245; TSOU P, 1995, J NON-CRYST SOLIDS, V186, P415, DOI 10.1016-0022-3093(95)00065-8; Yoldas BE, 2000, CHEM MATER, V12, P2475, DOI 10.1021-cm9903428; Zhou B, 2000, J VAC SCI TECHNOL B, V18, P2001, DOI 10.1116-1.1306279101949
Synthesis and Characterization of Mesoporous Hybrid Silica-Polyacrylamide Aerogels and Xerogels
No full textWe report the synthesis of highly porous hybrid silica-polyacrylamide aerogels where the inorganic network was obtained through the hydrolysis and poly-condensation of tetramethoxysilane via a two-step sol-gel process while the polyacrylamide polymer was made by photo-copolymerization of two organic monomers, the acrylamide and the bis-acrylamide. These aerogels were obtained after a carbon dioxide supercritical drying while the corresponding xerogels were dried by simple evaporation. These materials, as well as pure silica and polyacrylamide aerogels and xerogels, were characterized by FTIR spectroscopy, solid-state 29Si and 13C NMR spectroscopy, Thermogravimetric Analysis, a nitrogen adsorption-desorption technique, and Scanning Electron Microscopy. The FTIR and NMR spectra and the TGA-DTA analyses confirm the coexistence of highly branched silica and polyacrylamide networks reflecting the hybrid nature of the materials obtained. Nitrogen adsorption measurements reveal high specific surface areas and pore size distributions disclosing the mesoporous character of these hybrid materials. Hybrid silica-polyacrylamide aerogels having a specific surface area equal to 572 m 2-g and a pore volume 1.92 cm 3-g were successfully prepared for the first time in this study. The high porosity of these aerogels is due to a better resistance of the silica network to capillary forces during the supercritical drying when silica coexists with a polyacrylamide network. © 2010 Springer Science+Business Media B.V.Abramian L, 2009, CHEM ENG J, V150, P403, DOI 10.1016-j.cej.2009.01.019; Akl J, 2009, J MOL CATAL A-CHEM, V312, P18, DOI 10.1016-j.molcata.2009.06.026; Al-Oweini R, 2009, J MOL STRUCT, V919, P140, DOI 10.1016-j.molstruc.2008.08.025; Banet P, 2008, SENSOR ACTUAT B-CHEM, V130, P1, DOI 10.1016-j.snb.2007.07.103; BARRETT EP, 1951, J AM CHEM SOC, V73, P373, DOI 10.1021-ja01145a126; BERTOLUZZA A, 1982, J NON-CRYST SOLIDS, V48, P117, DOI 10.1016-0022-3093(82)90250-2; Brinker C. J., 1990, SOL GEL SCI PHYS CHE; Brunauer S, 1938, J AM CHEM SOC, V60, P309, DOI 10.1021-ja01269a023; Buisson P, 2001, J NON-CRYST SOLIDS, V285, P295, DOI 10.1016-S0022-3093(01)00470-7; Buisson P, 2006, J MOL CATAL B-ENZYM, V39, P77, DOI 10.1016-j.molcatb.2006.01.007; CANTIN M, 1974, NUCL INSTRUM METHODS, V118, P177, DOI 10.1016-0029-554X(74)90700-9; DURAN A, 1986, J NON-CRYST SOLIDS, V82, P391, DOI 10.1016-0022-3093(86)90156-0; Durme K. 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Mercury removal from aqueous solutions using silica, polyacrylamide and hybrid silica-polyacrylamide aerogels
No full textMercury(II) ions adsorption from aqueous solutions onto silica, polyacrylamide, and hybrid silica-polyacrylamide aerogels is studied. The aerogels structure was verified by FTIR spectroscopy and their texture by nitrogen adsorption. The adsorbents were tested under different experimental conditions where the effect of temperature, pH, contact time, initial mercury(II) concentration, and aerogels quantity were investigated. The mercury adsorption onto the three aerogels was shown to be very fast, with the fastest being performed at 45 °C onto the hybrid aerogels. pH 11 was revealed optimum indicating a superlative surface interaction between the adsorbent and the adsorbate. The adsorption kinetics follows a pseudo second-order pointing out the co-existence of chemisorption and physisorption with the intra-particle diffusion being the rate controlling step. The mercury(II) adsorption fits well with Langmuir adsorption isotherms where the polyacrylamide aerogels showed the highest adsorption capacity, followed by the hybrid aerogels. The regeneration of the aerogels at pH 2 and their reuse at pH 11 was conducted for three consecutive reuses where the adsorption capacity was successfully maintained. The hybrid aerogels were found to be the most economically interesting adsorbents due to their noticeable adsorptive capacity after regeneration coupled with their no-swelling behavior. © 2010 Elsevier B.V. All rights reserved.Abramian L, 2009, CHEM ENG J, V150, P403, DOI 10.1016-j.cej.2009.01.019; Aguado J, 2008, MICROPOR MESOPOR MAT, V109, P513, DOI 10.1016-j.micromeso.2007.05.061; Akkaya R, 2008, J HAZARD MATER, V151, P380, DOI 10.1016-j.jhazmat.2007.05.084; Aksu Z, 2008, CHEM ENG J, V142, P23, DOI 10.1016-j.cej.2007.11.005; Anirudhan TS, 2008, J HAZARD MATER, V157, P620, DOI 10.1016-j.jhazmat.2008.01.030; BARRET EP, 1951, J AM CHEM SOC, V73, P380; Barron-Zambrano J, 2004, J MEMBRANE SCI, V229, P179, DOI 10.1016-j.memsci.2003.10.028; Basha S, 2009, CHEM ENG J, V147, P226, DOI 10.1016-j.cej.2008.07.005; Belyakova LA, 2009, INORG CHIM ACTA, V362, P2222, DOI 10.1016-j.ica.2008.10.004; Brinker C. 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Corrigendum to Adsorption kinetics and thermodynamics of azo-dye Orange II onto highly porous titania aerogel [Chemical Engineering Journal 150 (2009) 403-410]
No full text[No abstract available]Abramian L, 2009, CHEM ENG J, V150, P403, DOI 10.1016-j.cej.2009.01.0190
Cobalt ferrite aerogels by epoxide sol-gel addition: Efficient catalysts for the hydrolysis of 4-nitrophenyl phosphate
No full textPorous cobalt ferrite aerogel catalysts were obtained by 1,2-epoxide sol-gel process and investigated in the hydrolysis of 4-nitrophenyl phosphate. These materials were synthesized by reacting cobalt and iron salts with propylene oxide in methanol, dried by supercritical carbon dioxide, and calcined between 200 and 800 °C. The catalysts were characterized using Fourier Transform Infrared (FTIR) spectroscopy, nitrogen adsorption-desorption technique, and powder X-ray diffraction (XRD). The as-prepared aerogel surface exhibits M-OH groups that disappear after annealing, which enhances the spinel structure. This was coupled with a better crystallinity revealed by XRD peaks sharpness. The crystallite sizes were found to be between 6.3 and 28.1 nm. In addition, the catalysts revealed high porosities that decrease as the annealing temperature increases. The catalysis showed that the catalytic activity significantly rely on the synthesis procedure and mainly the calcination temperature. Samples calcined at 600 °C and above did not show any catalytic activity, however, the highest catalytic efficiency was for those calcined at 200 °C with 100percent selectivity for the 4-nitrophenol. The correlation of the characterization techniques and the catalysis tests revealed that the catalytic properties of these sol-gel materials are due to the existence of residual surface OH groups. © 2009 Elsevier B.V. All rights reserved.Banerjee M, 2007, J MATER SCI, V 42, P1833, DOI 10.1007-s10853-006-0821-1; BARRETT EP, 1951, J AM CHEM SOC, V73, P373, DOI 10.1021-ja01145a126; Brinker CJ, 1990, PHYS CHEM SOL GEL PR; Brunauer S, 1938, J AM CHEM SOC, V60, P309, DOI 10.1021-ja01269a023; Calero-DdelC VL, 2007, J MAGN MAGN MATER, V314, P60, DOI 10.1016-j.jmmm.2006.12.030; Cote LJ, 2003, FLUID PHASE EQUILIBR, V210, P307, DOI 10.1016-S0378-3812(03)00168-7; El-Shobaky HG, 2007, MAT SCI ENG B-SOLID, V143, P21, DOI 10.1016-j.mseb.2007.07.072; Gao YP, 2007, CHEM MATER, V19, P6007, DOI 10.1021-cm0718419; Gash AE, 2001, J NON-CRYST SOLIDS, V285, P22, DOI 10.1016-S0022-3093(01)00427-6; Giinzler H., 2002, IR SPECTROSCOPY INTR; Gu ZJ, 2008, J PHYS CHEM C, V112, P18459, DOI 10.1021-jp806682q; Gul IH, 2008, J ALLOY COMPD, V465, P227, DOI 10.1016-j.jallcom.2007.11.006; HAMDEH HH, 1994, J APPL PHYS, V76, P1135, DOI 10.1063-1.357835; Hua ZH, 2007, J ALLOY COMPD, V427, P199, DOI 10.1016-j.jallcom.2006.02.048; Huesing N, 1995, J NONCRYST SOLIDS, V186, P37; Lavela P, 2007, J POWER SOURCES, V172, P379, DOI 10.1016-j.jpowsour.2007.07.055; Lee H, 2008, CATAL LETT, V124, P364, DOI 10.1007-s10562-008-9476-7; Liu T, 2008, MATER LETT, V62, P4056, DOI 10.1016-j.matlet.2008.04.081; LIVAGE J, 1988, PROG SOLID STATE CH, V18, P259, DOI 10.1016-0079-6786(88)90005-2; Lowell S., 2004, CHARACTERIZATION POR; Maaz K, 2007, J MAGN MAGN MATER, V308, P289, DOI 10.1016-j.jmmm.2006.06.003; Manova E, 2004, CHEM MATER, V16, P5689, DOI 10.1021-cm049189u; Mathew T, 2004, APPL CATAL A-GEN, V273, P35, DOI 10.1016-j.apcata.2004.06.011; Meron T, 2005, J MAGN MAGN MATER, V292, P11, DOI 10.1016-j.jmmm.2004.10.084; Patterson AL, 1939, PHYS REV, V56, P978, DOI 10.1103-PhysRev.56.978; Pierre AC, 2002, CHEM REV, V102, P4243, DOI 10.1021-cr0101306; Ramankutty CG, 2002, J MOL CATAL A-CHEM, V187, P105, DOI 10.1016-S1381-1169(02)00121-8; Sisk CN, 2008, J MATER CHEM, V18, P2607, DOI 10.1039-b802174k; Sun SH, 2004, J AM CHEM SOC, V126, P273, DOI 10.1021-ja0380852; Thang PD, 2007, J MAGN MAGN MATER, V310, P2621, DOI 10.1016-j.jmmm.2006.11.048; Toksha BG, 2008, SOLID STATE COMMUN, V147, P479, DOI 10.1016-j.ssc.2008.06.040; Toledo-Antonio JA, 2002, APPL CATAL A-GEN, V234, P137, DOI 10.1016-S0926-860X(02)00212-0; Vijayaraj M, 2006, J CATAL, V241, P83, DOI 10.1016-j.jcat.2006.04.010; WALDRON RD, 1955, PHYS REV, V99, P1727, DOI 10.1103-PhysRev.99.1727; Wang CC, 2006, J MAGN MAGN MATER, V304, pE451, DOI 10.1016-j.jmmm.2006.02.064; Wang X, 2005, NATURE, V437, P121, DOI 10.1038-nature03968; Xu R, 2003, CHEM MATER, V15, P2040, DOI 10.1021-cm021732o; Yan CH, 1999, SOLID STATE COMMUN, V111, P287, DOI 10.1016-S0038-1098(99)00119-2; Zhao LJ, 2008, J SOLID STATE CHEM, V181, P245, DOI 10.1016-j.jssc.2007.10.0348101
Immobilized polyoxometalates onto mesoporous organically-modified silica aerogels as selective heterogeneous catalysts of anthracene oxidation
No full textImmobilized molybdovanadophosphoric acids onto organically surface-modified silica aerogels were successfully prepared and investigated in heterogeneous catalysis of anthracene oxidation. The catalysts were obtained by supporting mono- and di-vanadium substituted molybdophosphoric acids on hybrid silica materials synthesized via the sol-gel process followed by surface amino-functionalization. The FTIR, DR UV-vis, and AA spectroscopy confirmed the loading and distribution of the polyoxometalate molecules on the surface of the aerogels. The nitrogen adsorption-desorption technique revealed a systematic decrease in the specific surface area and pore volume after the immobilization of the polyoxometalates. The application of the supported molecules as catalysts for anthracene oxidation showed 100percent selectivity for 9,10- anthraquinone as opposed to the reactions conducted under homogeneous conditions. Moreover, at certain conditions, the catalytic activity of the supported polyoxometalates was greater than their corresponding free polyoxometalates with a clear effect of the surface chemical groups of the supporting silica aerogels. Additionally, the oxidant and solvent nature showed a crucial effect on the catalytic activity and selectivity of the immobilized polyoxometales. The heterogeneous catalysts were regenerated and reused over consecutive catalytic cycles reflecting a potential economic interest in these materials besides their high efficiency in heterogeneous catalysis. © Springer Science+Business Media, LLC 2011.Al-Kadamany G, 2010, CHEM-EUR J, V16, P11797, DOI 10.1002-chem.201000786; Al-Oweini R, 2009, J MOL STRUCT, V919, P140, DOI 10.1016-j.molstruc.2008.08.025; Al-Oweini R, 2010, APPL SURF SCI, V257, P276, DOI 10.1016-j.apsusc.2010.06.086; Antonova NS, 2010, J AM CHEM SOC, V132, P7488, DOI 10.1021-ja1023157; BARRETT EP, 1951, J AM CHEM SOC, V73, P373, DOI 10.1021-ja01145a126; Bassil BS, 2011, ANGEW CHEM INT EDIT, V50, P5961, DOI 10.1002-anie.201007617; Berzelius J.J., 1826, POGGENDORFS ANN PHYS, V6, P369; Bi LH, 2009, INORG CHEM, V48, P10068, DOI 10.1021-ic9009306; Bordoloi A, 2007, J CATAL, V247, P166, DOI 10.1016-j.jcat.2007.01.020; Bordoloi A, 2008, J CATAL, V259, P232, DOI 10.1016-j.jcat.2008.08.010; Brinker C. J., 1990, SOL GEL SCI PHYS CHE; Brunauer S, 1938, J AM CHEM SOC, V60, P309, DOI 10.1021-ja01269a023; Cairns D, 2002, BIOORGAN MED CHEM, V10, P803, DOI 10.1016-S0968-0896(01)00337-6; Chen QL, 2008, CHEM ENG PROCESS, V47, P787, DOI 10.1016-j.cep.2006.12.012; Donoeva BG, 2010, EUR J INORG CHEM, V33, P5312; Durand N, 2011, LANGMUIR, V27, P4057, DOI 10.1021-la1048826; Ge P, 1997, TETRAHEDRON, V53, P17469, DOI 10.1016-S0040-4020(97)10195-8; Giinzler H., 2002, IR SPECTROSCOPY INTR; Guo YH, 2000, CHEM MATER, V12, P3501, DOI 10.1021-cm000074+; Hu CW, 1996, CHEM COMMUN, P121, DOI 10.1039-cc9960000121; Huang HS, 2003, J MED CHEM, V46, P3300, DOI 10.1021-jm0204921; Huesing N, 1995, J NONCRYST SOLIDS, V186, P37; ISHII Y, 1988, J ORG CHEM, V53, P3587, DOI 10.1021-jo00250a032; Izumi Y, 1995, MICROPOROUS MATER, V5, P255, DOI 10.1016-0927-6513(95)00059-3; Jahier C, 2009, EUR J INORG CHEM, P5148, DOI 10.1002-ejic.200900682; Joseph T, 2005, J MOL CATAL A-CHEM, V229, P241, DOI 10.1016-j.molcata.2004.12.008; Katsoulis DE, 1998, CHEM REV, V98, P359, DOI 10.1021-cr960398a; Keggin JF, 1933, NATURE, V131, P908, DOI 10.1038-131908b0; Kumar D, 2007, MICROPOR MESOPOR MAT, V98, P309, DOI 10.1016-j.micromeso.2006.09.023; Long DL, 2007, CHEM SOC REV, V36, P105, DOI 10.1039-b502666k; Maksimchuk NV, 2007, J CATAL, V246, P241, DOI 10.1016-j.jcat.2006.11.026; Manisankar P, 2005, J MOL CATAL A-CHEM, V232, P45, DOI 10.1016-j.molcata.2005.01.001; Mizuno N, 1998, CHEM REV, V98, P199, DOI 10.1021-cr960401q; Pierre AC, 2002, CHEM REV, V102, P4243, DOI 10.1021-cr0101306; Pozniczek J, 2006, APPL CATAL A-GEN, V298, P217, DOI 10.1016-j.apcata.2005.10.013; Santacesaria E, 1999, CHEM ENG SCI, V54, P2799, DOI 10.1016-S0009-2509(98)00377-7; Selvaraj M, 2007, MICROPOR MESOPOR MAT, V101, P240, DOI 10.1016-j.micromeso.2006.12.020; Song H, 2006, J AM CHEM SOC, V128, P3027, DOI 10.1021-ja057383r; Strukul G, 1992, CATALYTIC OXIDATIONS, P1; TSIGDINO.GA, 1968, INORG CHEM, V7, P437, DOI 10.1021-ic50061a00933
Liesegang banding and multiple precipitate formation in cobalt phosphate systems
No full textWe study a cobalt phosphate Liesegang pattern from cobalt(II) and phosphate ions in a 1D tube. The system yields a complex, multi-component pattern. Characterization of the different precipitates by FTIR, SEM and XRD reveals that they are cobalt phosphate polymorphs with different degrees of hydration. © 2012 Elsevier B.V. All rights reserved.Al-Ghoul M, 2001, J PHYS CHEM A, V105, P8053, DOI 10.1021-jp011158o; Andreev S., 1960, ZH STRUKT KHIM, V1, P183; Badsar M, 2010, MATER RES BULL, V45, P1080, DOI 10.1016-j.materresbull.2010.06.022; Bohm F, 2003, PALAEOGEOGR PALAEOCL, V189, P161, DOI 10.1016-S0031-0182(02)00639-9; Burgess J., 1999, IONS SOLUTION BASIC; Corbeil M.C., 2002, STUD CONSERV, V47, P47; DAS I, 1989, J PHYS CHEM-US, V93, P7269, DOI 10.1021-j100357a047; DAS I, 1990, J PHYS CHEM-US, V94, P8968, DOI 10.1021-j100389a023; DAS I, 1991, J PHYS CHEM-US, V95, P3866, DOI 10.1021-j100162a078; Dzyuba E., 1973, J APPL SPECTROSC, V12, P666; El-Rassy H., 2008, J PHYS CHEM A, V112, P775; Feng PY, 1997, J AM CHEM SOC, V119, P2497, DOI 10.1021-ja9634841; Greenwood N. N., 1997, CHEM ELEMENTS; Henisch H., 1988, CRYSTALS GELS LIESEG; Jamtveit B., 1999, GROWTH DISSOLUTION P, P65; Jonynaite D, 2009, CHEMIJA, V20, P10; Kagawa M, 1999, SEKIYU GAKKAISHI, V42, P258; Kanan MW, 2009, CHEM SOC REV, V38, P109, DOI 10.1039-b802885k; Kim TR, 2007, J PHYS CHEM SOLIDS, V68, P1203, DOI 10.1016-j.jpcs.2007.03.027; Liesegang R. E., 1896, CHEM FERNWIRKUNG LIE, V37, P305; Liesegang R. E., 1896, NATURWISS WOCHENSCHR, V11, P353; Liesegang R.E., 1896, CHEM FERNWIRKUNG LIE, V37, P331; Msharrafieh M, 2005, CHEMPHYSCHEM, V6, P2647, DOI 10.1002-cphc.200500199; Ortoleva P. J., 1994, OXFORD MONOGRAPHS GE, V23; Salvetat, 1859, CR HEBD ACAD SCI, V48, P295; Socrates G., 2001, INFRARED RAMAN CHARA; SOKOLOV ND, 1955, USP FIZ NAUK+, V57, P205; SULTAN R, 1993, PHYSICA D, V63, P202, DOI 10.1016-0167-2789(93)90155-T; Sultan RF, 2000, PHYS CHEM CHEM PHYS, V2, P3155, DOI 10.1039-b001221l; Wen H, 2008, J PHYS CHEM C, V112, P15948, DOI 10.1021-jp804602b34
Mechanism of revert spacing in a PbCrO 4 Liesegang system
No full textPeriodic precipitation of sparingly soluble salts yields parallel Liesegang bands in 1D whose spacings obey either one of two known trends. The overwhelming trend is an increase in spacing as we move away from the junction, while some systems display a decrease in spacing as the bands get further away from the interface. The latter trend is much less common and is known as the revert spacing law. Whereas the direct (normal) spacing law is generally well-undertsood, the revert spacing trend has not been explicitly and distinctly elucidated. In this paper, we propose a mechanism of revert spacing governed by the adsorption of the diffusing CrO 4 2- ions on the formed PbCrO 4 Liesegang bands and carry out a set of experiments that support the suggested scenario. It is shown that this adsorption increases as the band number (n) increases in revert spacing systems, while it decreases as n increases in direct spacing systems. It is concluded that this correlation in opposite directions decisively reveals the role of adsorption in the mechanism. The attraction between the CrO 4 2- and Pb 2+ in the gel causes the bands to form gradually closer and closer. Secondary structure (thinner bands formed within the main ones) obtained under some conditions is discussed in view of the light sensitivity of the chromate ion and the stability of the lead chromate sol. © 2011 American Chemical Society.Antal T, 2007, PHYS REV E, V76, DOI 10.1103-PhysRevE.76.046203; CAHN JW, 1958, J CHEM PHYS, V28, P258, DOI 10.1063-1.1744102; DAS I, 1987, J PHYS CHEM-US, V91, P747, DOI 10.1021-j100287a051; DAS I, 1987, J CRYST GROWTH, V84, P231, DOI 10.1016-0022-0248(87)90135-7; DAS I, 1987, J CRYST GROWTH, V82, P361, DOI 10.1016-0022-0248(87)90326-5; DOUNIN MS, 1928, KOLLOID Z, V48, P167; FEENEY R, 1983, J CHEM PHYS, V78, P1293, DOI 10.1063-1.444867; FLICKER M, 1974, J CHEM PHYS, V60, P3458, DOI 10.1063-1.1681560; Ghosh D. N., 1930, J INDIAN CHEM SOC, V7, P509; HANTZ P, 2002, PHYS CHEM CHEM PHYS, V4, P1; HEDGES ES, 1928, J CHEM SOC, V129, P2714; HOLBA V, 1989, COLLOID POLYM SCI, V267, P456, DOI 10.1007-BF01410193; Isemura T., 1933, Bulletin of the Chemical Society of Japan, V8, DOI 10.1246-bcsj.8.11; Isemura T., 1933, Bulletin of the Chemical Society of Japan, V8, DOI 10.1246-bcsj.8.108; Jablczynski CK, 1923, B SOC CHIM FR, V33, P1592; KANNIAH N, 1981, J COLLOID INTERF SCI, V80, P369, DOI 10.1016-0021-9797(81)90195-8; KANNIAH N, 1984, P INDIAN AS-CHEM SCI, V93, P801; KANT K, 1963, KOLLOID Z Z POLYM, V191, P145, DOI 10.1007-BF01499541; Liesegang R. E., 1896, NATURWISS WOCHENSCHR, V11, P353; Mathur P. B., 1957, KOLLOID Z, V159, P143; MEHTA B, 1964, KOLLOID Z Z POLYM, V209, P54; MEHTA B, 1965, KOLLOID Z Z POLYM, V209, P58; MULLER SC, 1982, J PHYS CHEM-US, V86, P4078; Ostwald W, 1900, Z PHYS CHEM-STOCH VE, V34, P495; DAS I, 1988, J NON-EQUIL THERMODY, V13, P209, DOI 10.1515-jnet.1988.13.3.209; Ramaiah K.S., 1939, Proceedings of the Indian Academy of Sciences, Section A, V9; Ratke L., 2002, GROWTH COARSENING OS; Shreif Z, 2004, PHYS CHEM CHEM PHYS, V6, P3461, DOI [10.1039-b404064c, 10.1039-b404074c]; Stern K., 1954, CHEM REV, V54, P81; Sultan R, 1996, J PHYS CHEM-US, V100, P16912, DOI 10.1021-jp960958+11121
Política Institucional de Innovación
No full textEsstablece los lineamientos y el marco normativo para promover, gestionar y consolidar una cultura de innovación dentro de la institución, articulada a sus funciones sustantivas de formación, investigación y responsabilidad social. La política reconoce la importancia del cambio, la creatividad, la colaboración y la apertura a nuevas ideas como pilares para la transformación institucional, buscando generar impacto en la calidad de vida de la comunidad universitaria y contribuir al desarrollo social y humano, tanto a nivel local como nacional. Además, el documento describe la estructura organizacional responsable, los principios, criterios de gestión y los mecanismos de evaluación que garantizan la implementación y mejora continua de las acciones innovadoras, en coherencia con el Proyecto Educativo Institucional y el Plan de Desarrollo Institucional
Reaction-diffusion based co-synthesis of stable α- and β-cobalt hydroxide in bio-organic gels
No full textWe report the preparation, dynamics of formation and extensive characterization of a stable two-phase system of crystalline α- and β-Co(OH)2. The method is based on the reaction and diffusion of hydroxide ions into a biopolymer gel (agar, gelatin) containing Co(II). The spatio-temporal dynamics leading to the formation and coexistence of two polymorphs exhibit a complicated and rich pattern whereby the system proceeds as a propagating Ostwald ripening front that continuously transforms blue-green α-Co(OH)2 to crystalline β-Co(OH)2. Depending on the nature of the gel, the system might further exhibit fascinating Liesegang bands. The coexisting polymorphs were characterized using XRD, FTIR, UV-vis, TGA, SEM and TEM, and EPR. The FTIR spectra reveal the intercalation of water molecules and chloride ions between the hydroxyl layers in the case of α-Co(OH)2. X-ray diffraction and electronic microscopy investigations confirm the aforementioned Ostwald ripening process during the phase transformation whereby almost-amorphous α-Co(OH)2 dissolves to form crystalline β-Co(OH)2 5 μm in length. The UV-vis reflectance spectra reveal that the origin of the blue-green color in the α-polymorph is due to the tetrahedrally coordinated Co(II) ions existing within the octahedral Co(II) layers. The reorganization of these tetrahedral Co(II) ions in the α-polymorph to form octahedral Co(II) in the β-polymorph is shown to take place in seconds without induction time. α-Co(OH)2 was found to be mesoporous while the β-polymorph is microporous with low nitrogen adsorption capacities. Due to dipole-dipole broadening, no EPR spectrum was obtained for the β-polymorphs even at low temperature. In contrast, the obtained EPR spectrum of the α-polymorph was consistent with that of Co(II) in various materials. © 2009 Elsevier B.V. All rights reserved.Abragam A., 1970, ELECT PARAMAGNETIC R; Benson P., 1964, ELECTROCHIM ACTA, V9, P275, DOI 10.1016-0013-4686(64)80016-5; BISH DL, 1981, MINERAL MAG, V44, P339, DOI 10.1180-minmag.1981.044.335.15; Brayner R, 2007, CHEM MATER, V19, P1190, DOI 10.1021-cm062580q; Cage B, 1998, J MAGN RESON, V135, P178, DOI 10.1006-jmre.1998.1569; Cao L, 2004, ADV MATER, V16, P1853, DOI 10.1002-adma.200400183; Dixit M, 1996, J MATER CHEM, V6, P1429, DOI 10.1039-jm9960601429; Du Y, 2008, J MATER CHEM, V18, P4450, DOI 10.1039-b809085h; Duval C, 1963, INORGANIC THERMOGRAV; El-Batlouni H, 2008, J PHYS CHEM A, V112, P7755, DOI 10.1021-jp804569b; Elumalai P, 2001, J POWER SOURCES, V93, P201, DOI 10.1016-S0378-7753(00)00572-3; Gaunand A, 2002, POWDER TECHNOL, V128, P332, DOI 10.1016-S0032-5910(02)00276-0; ISBER S, 1995, PHYS REV B, V51, P15211, DOI 10.1103-PhysRevB.51.15211; Itahara H, 2004, J MATER CHEM, V14, P61, DOI 10.1039-b309804d; Jayashree RS, 1999, J MATER CHEM, V9, P961, DOI 10.1039-a807000h; Kamath PV, 1997, J SOLID STATE CHEM, V128, P38, DOI 10.1006-jssc.1996.7144; Lever A.B.P., 1984, INORGANIC ELECT SPEC; Liesegang R. E., 1896, NATURWISS WOCHENSCHR, V11, P353; Liu ZP, 2005, J AM CHEM SOC, V127, P13869, DOI 10.1021-ja0523338; Ma RZ, 2006, INORG CHEM, V45, P3964, DOI 10.1021-ic052108r; Muller SC, 2003, J PHYS CHEM A, V107, P7997, DOI 10.1021-jp030364o; OLIVA P, 1982, J POWER SOURCES, V8, P229, DOI 10.1016-0378-7753(82)80057-8; OOKUBO A, 1993, LANGMUIR, V9, P1418, DOI 10.1021-la00029a042; Ostwald S. Z., 1897, Z PHYS CHEM, V22, P289; Poul L, 2000, CHEM MATER, V12, P3123, DOI 10.1021-cm991179j; REICHLE WT, 1986, SOLID STATE IONICS, V22, P135, DOI 10.1016-0167-2738(86)90067-6; Rujiwatra A, 2001, J AM CHEM SOC, V123, P10584, DOI 10.1021-ja0109848; STAHLIN W, 1970, ACTA CRYSTALL B-STRU, VB 26, P860, DOI 10.1107-S0567740870003230; Zhang JG, 2004, J AM CHEM SOC, V126, P7908, DOI 10.1021-ja031523k; Zhu YC, 2002, J MATER CHEM, V12, P729, DOI 10.1039-b107750c12121
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